In a gas turbine engine the bearing compartment must be sealed from the higher pressure and higher temperature environment of the turbine gas flow. Carbon seals are frequently used and because of the high speed rotation of the gas turbine engine, such seals must be lubricated to minimize friction and wear as well as to provide some cooling.
For this purpose oil is delivered to slight recesses in the interface between the seal and seal plate. The higher gas pressure is located at the inner diameter of the seal. Despite centrifugal force and gas pressure tending to urge the oil out from the seal into the bearing chamber some oil finds its way into the gas side of the seal. If this oil finds its way into the main gas flow, it will cause contamination of the blading and/or fires. It is important therefore, to return this oil to the bearing chamber.
U.S. Pat. No. 4,406,459 to Joseph Davis et al issued Sept. 27, 1983 is directed to returning the weepage oil to the bearing chamber. An inwardly facing annulus is formed at the interface between the carbon seal and the seal plate with centrifugal forces retaining a pool of oil within this annulus. Oil passages are provided passing through the seal plate from the location in the annulus to a radially outward position so that these passages operate as a pump to centrifugally pump oil from the annulus area.
Testing has shown that with this arrangement not all of the oil is returned. In some manner a portion of the oil flow, possibly in the form of a spray, is carried into the main gas flow of the gas turbine.